The invention relates to an optical lens system for use in an optical scanning device for scanning an optically scannable record carrier, which lens system comprises a first lens, a second lens, which is relatively small in comparison with the first lens and, in operation, is positioned between the first lens and the record carrier, and a lens holder accommodating the two lenses.
The invention also relates to an optical scanning device for scanning an optically scannable record carrier, which scanning device comprises a radiation source, an optical lens system having an optical axis for focusing a radiation beam supplied, in operation, by the radiation source to a scanning spot on the record carrier, and an actuator for displacing the lens system parallel to the optical axis, the lens system comprising a first lens, a second lens, which is relatively small in comparison with the first lens and, in operation, is positioned between the first lens and the record carrier, and a lens holder accommodating the two lenses.
The invention also relates to an optical player comprising a table which is rotatable about an axis of rotation, a displacement device and an optical scanning device for scanning an optically scannable record carrier which can be placed on the table, the scanning device comprising a radiation source, an optical lens system having an optical axis for focusing a radiation beam supplied, in operation, by the radiation source to a scanning spot on the record carrier, and an actuator for displacing the lens system parallel to the optical axis, the lens system comprising a first lens, a second lens, which is relatively small in comparison with the first lens and, in operation, is positioned between the first lens and the record carrier, and a lens holder accommodating the two lenses, at least the lens system of the scanning device being displaceable by means of the displacement device substantially in a radial direction relative to the axis of rotation.
An optical lens system, an optical scanning device, and an optical player of the types referred to in the opening paragraphs are known from EP-A-0 863 502. The first lens of the known lens system is a main lens or objective lens, whilst the second lens is a relatively small auxiliary lens which, in operation, is positioned between the main lens and the record carrier to be scanned. By using the auxiliary lens, the known lens system has a relatively large numerical aperture. As a result, the radiation beam, which, in operation, is generated by the radiation source of the known optical scanning device in which the known optical lens system is used, is focused by the lens system to a relatively small scanning spot on the record carrier. The known scanning device and the known optical player, in which the known scanning device is used, are thus suitable for scanning record carriers having relatively small elementary information characteristics, i.e. record carriers having a relatively high information density. The known scanning device and the known optical player are therefore particularly suitable for scanning record carriers in accordance with the so-termed DVR-system. The two lenses of the known optical system are made of glass. Upon manufacture of the optical lens system, the two lenses are separately arranged in the lens holder. In order to obtain an adequate optical accuracy of the lens system, the optical axes of the two lenses must coincide within predetermined, relatively close tolerances. In order to obtain such accurate positions of the lenses in the lens holder, the two lenses must be aligned relative to each other by means of suitable aligning tools during assembly of the lens system.
One drawback of the known lens system, the known optical scanning device and the known optical player is that the assembly of the lens system is relatively complicated, because the lens system comprises at least three separate parts, i.e. the lens holder and the two lenses, each of which needs to be produced separately first, and because the two lenses must be aligned relative to each other.
It is an object of the invention to provide an optical lens system, an optical scanning device and an optical player of the types referred to in the opening paragraphs, in which the lens system can be manufactured in a considerably simplified manner, whilst the lens system has an optical accuracy which, also in operation, is at least as high as the optical accuracy of the known lens system.
In order to achieve this object, an optical lens system according to the invention is characterized in that the lens holder and one of the two lenses are manufactured as one single integrated part from a transparent synthetic material by means of a moulding process, whilst the other lens is arranged in the integrated part as a separate component, with a chamber enclosed by the two lenses and the lens holder communicating with the environment of the lens system via an air vent connection.
In order to achieve this object, an optical scanning device according to the invention is characterized in that the lens system used therein is an optical lens system according to the invention.
In order to achieve this object, an optical player according to the invention is characterized in that the optical scanning device used therein is an optical scanning device according to the invention.
Since the lens holder and one of the two lenses are manufactured as one single integrated part from a transparent synthetic material by means of a moulding process, with the other lens being arranged as a separate component in the integrated part, only two parts need to be mutually assembled during assembly of the lens system according to the invention. The integrated part can be manufactured in a very accurate manner by means of the moulding process. The integrated part may be provided, for example, with a lens mount and/or a positioning surface for the other lens being accurately positioned with respect to the integrated lens, so that the other lens can be accurately positioned with respect to the integrated lens in the integrated part in a very simple manner. This leads to a considerable simplification of the assembly of the lens system according to the invention and obviates the need to align the lenses relative to each other. Since the chamber enclosed by the two lenses and the lens holder communicates with the environment of the lens system via an air vent connection, an increase of the air pressure in the aforesaid chamber is prevented in operation. Without the use of the air vent connection, such an increase of the air pressure would result from an increase of the ambient temperature of the lens system. Since the integrated lens of synthetic material is considerably less stiff than a lens which is made of glass, such an increase of the air pressure would lead to deformations of the integrated lens, which in turn would lead to an unacceptable decrease of the optical accuracy of the lens system. Since such deformations of the integrated lens are prevented in this manner, the lens system according to the invention has an optical accuracy which, also in operation, is at least as high as the optical accuracy of a lens system which only comprises glass lenses. Another advantage of the lens system according to the invention is the fact that the lens system has a relatively low mass, due to the use of the lens of synthetic material. In a special embodiment of the lens system according to the invention, said mass is further reduced by making the other lens of synthetic material as well. This leads to a considerable reduction of the forces required for displacing the lens system, as a result of which the scanning speeds of the scanning device and the player according to the invention can be considerably increased.
A special embodiment of an optical lens system according to the invention is characterized in that the integrated part comprises the lens holder and the second lens. Since the second lens is relatively small in comparison with the first lens, the second lens in itself would be more difficult to handle than the first lens during assembly of the lens system. Since the integrated part comprises the second lens in this special embodiment, the advantage of a simple assembly, which the invention offers in a general sense, is used optimally in this embodiment.
Another embodiment of an optical lens system according to the invention is characterized in that the integrated part is provided with a circular cylindrical lens mount for the other lens, which lens mount has a center line which substantially coincides with an optical axis of the lens that forms part of the integrated part, whilst the other lens makes up more than one half of a substantially spherical lens body of glass with a diameter which is substantially equal to a diameter of the lens mount. Since the diameter of the aforesaid spherical lens body is substantially equal to the diameter of the aforesaid circular cylindrical lens mount, the other lens is accurately positioned in the lens mount in directions perpendicular to the center line. Since the lens mount forms part of the integrated part, the lens mount can be arranged in the integrated part in a relatively simple and very accurate manner by means of the moulding process, so that the center line of the lens mount accurately coincides with the optical axis of the integrated lens. As a result, the other lens is accurately positioned relative to the integrated lens in directions perpendicular to the center line. Since the other lens makes up more than one half of the aforesaid spherical lens body, the other lens can still be tilted through limited angles about the center of the lens body after being placed in the lens mount without influencing the position of the other lens in directions perpendicular to the center line. As a result, the accurate position of the other lens relative to the integrated lens in directions perpendicular to the center line will not be affected when the other lens is tilted by means of suitable aligning tools after being placed in the lens mount for the purpose of aligning the optical axis of the other lens with the optical axis of the integrated lens. The spherical, glass lens body can be manufactured in a relatively simple, very accurate manner by means of, for example, a rolling process.
Yet another embodiment of an optical lens system according to the invention is characterized in that the integrated part is provided with a positioning surface for the other lens, which extends substantially perpendicularly to the center line and bounds the lens mount, whilst the spherical lens body of the other lens is provided with a boundary surface on a side facing the lens that forms part of the integrated part, via which boundary surface the other lens abuts against the positioning surface. Since said positioning surface forms part of the integrated part, the positioning surface can be arranged in the integrated part in a relatively simple and very accurate manner by means of the moulding process. The optical axis of the other lens extends perpendicularly to the aforesaid boundary surface of the spherical lens body. Since the other lens abuts with said boundary surface against the positioning surface, which has been accurately arranged perpendicularly to the center line and perpendicularly to the optical axis of the integrated lens by means of the moulding process, the optical axes of the two lenses of the lens system extend accurately parallel to each other after the other lens has been placed in abutment with the positioning surface, thus obviating the need to align the other lens.
A special embodiment of an optical lens system according to the invention is characterized in that the positioning surface adjoins the lens mount via a recess formed in the positioning surface. When the other lens is being placed in the circular cylindrical lens mount during assembly of the lens system, an outer circumference of the spherical lens body of the other lens is slid into the lens mount without play. As a result, dust particles that are present on the lens mount are carried along by the other lens and, owing to friction, particles are even detached from the lens mount. Since the aforesaid recess is formed at the location where the circular cylindrical lens mount joins the positioning surface, i.e. at the location where the other lens slides along the lens mount during assembly, substantially all the aforesaid dust particles and detached particles are collected in said recess. After the other lens has been placed in abutment with the positioning surface, said recess is closed by the boundary surface of the spherical lens body, so that the released particles are likewise confined.
Another embodiment of an optical lens system according to the invention is characterized in that the integrated part is provided with a lens mount for the other lens having the shape of a segment of a sphere, which lens mount has a center which lies on an optical axis of the lens that forms part of the integrated part, whilst the other lens comprises a lens body substantially having the shape of a segment of a sphere, which has a radius which is substantially equal to a radius of the lens mount. Since the lens mount having the shape of a segment of a sphere forms part of the integrated part, said lens mount can be arranged in the integrated part in a relatively simple and very accurate manner by means of the moulding process, so that the center of the lens mount is accurately positioned on the optical axis. Since the radius of the aforesaid lens body of the other lens having the shape of a segment of a sphere is substantially equal to the radius of the lens mount having the shape of a segment of a sphere, the other lens is accurately positioned in the lens mount in directions perpendicular to the optical axis of the integrated lens. After being placed in the lens mount, the other lens can still be tilted through limited angles about the center of the lens mount in said lens mount without influencing the position of the other lens in directions perpendicular to the optical axis of the integrated lens. As a result, the accurate position of the other lens relative to the integrated lens in directions perpendicular to the aforesaid optical axis will not be affected if the other lens is tilted by means of suitable aligning tools after being placed in the lens mount for the purpose of aligning the optical axis of the other lens with the optical axis of the integrated lens.
Yet another embodiment of an optical lens system according to the invention is characterized in that the air vent connection comprises at least one groove-like channel formed in a surface of the lens mount. Said channel is formed in the integrated part during the moulding process by providing the mould that is used in the moulding process with an elevation at the position of the channel. The air vent connection is thus provided in a very practical and simple manner.
A special embodiment of an optical lens system according to the invention is characterized in that the air vent connection comprises at least one groove-like channel formed in a surface of the lens mount and at least one groove-like channel formed in the positioning surface, which channels both open into the recess. In this special embodiment, in which the other lens abuts against the positioning surface with its boundary surface, the air vent connection is made up in a practical and efficient manner of the groove-like channel in the surface of the lens mount, the recess formed in the positioning surface and the groove-like channel in the positioning surface. In this embodiment, the air vent connection is likewise provided in the integrated part during the moulding process.
Another embodiment of an optical lens system according to the invention is characterized in that the integrated part is provided, near the lens that forms part of the integrated part, with a transparent window extending substantially perpendicularly to an optical axis of said lens, via which window the enclosed chamber is optically accessible from the environment of the lens system. Said window is formed in the integrated part in a simple manner during the moulding process by providing the mould used in the moulding process with an optically smooth surface at the position of the window. Via said window, the position of the boundary surface of the spherical lens body of the other lens can be measured in a practical manner by means of optical measuring equipment when the optical axis of the other lens is aligned with the optical axis of the integrated lens.
Yet another embodiment of an optical lens system according to the invention is characterized in that the integrated part is provided, near the lens that forms part of the integrated part, with a protective element which extends beyond the aforesaid lens, parallel to an optical axis of said lens. Said protective element protects the integrated lens in operation against unwanted contact with the record carrier and is provided in the integrated part in a simple manner during the moulding process by providing the mould used in the moulding process with a portion which is recessed relative to the integrated lens at the position of the protective element.
A special embodiment of an optical lens system according to the invention is characterized in that the lens that forms part of the integrated part is provided with a substantially circular optical boundary surface extending substantially perpendicularly to an optical axis of said lens, a center of which optical boundary surface is spaced apart from the optical axis by a distance which is larger than the radius of a radiation beam which, in operation, is present in the optical boundary surface. Said optical boundary surface is provided in the integrated part in a simple manner during the moulding process by providing the mould used in the moulding process with a circular, optically smooth surface at the position of the optical boundary surface. Such an optically smooth surface is formed in the mould by means of a precision lathe. As a result of this operation, an unavoidable irregularity is formed in the surface in the center of the optically smooth surface. Since said center is spaced apart from the optical axis by a distance which is larger than the radius of the radiation beam which, in operation, is present in the optical boundary surface, the presence of the irregularity in the optical boundary surface resulting from the aforesaid irregularity in the mould in the radiation beam in operation, which might cause an optical error of the integrated lens, is prevented in this special embodiment.
These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.